The state's population growth over the past five years has slowed to a relative trickle, which seems evident given the economy. But newly-certified figures released by Portland State University's Population Research Center show the recession's lingering effect.

Natural increase -- births outnumbering deaths -- accounted for two-thirds of the state's population growth in the year that ended June 30, 2011. That's a reversal of how we grew from the 1990s through 2008, when natural increase typically made up only a quarter or third of annual growth. The rest came from net migration -- people moving in minus people moving out.

People tend to stay put when the economy is bad, said Risa Proehl, manager of PSU's population estimates program. It costs to move, employers are less likely to pay for it and -- in Oregon's case -- the state hasn't offered much of a job market the past couple years.

For the record, Oregon had 3,856,815 people as of July 1. That's 0.5 percent more than on the same date in 2010, which marked the slowest growth since the 1980s, Proehl said.

Oregon has added an average of 41,000 people per year from 2000-2010. That's akin to adding a new Albany every year. But the population growth of the past year was slightly below 20,000 -- like adding a new Milwaukie.

The numbers hold some surprises, and link again to the economy.

Oregon counted 100,000 fewer licensed drivers in 2011 than the previous year. "If you only look at the number of driver's licenses issued, it looks like a huge population loss," Proehl said.

Other data showed that wasn't the case, so Proehl wondered if the decline indicated an aging population was giving up the right to drive. Some of that occurred, of course, but not enough to explain the huge drop in licensed drivers, she said.

Instead, she believes it's the economy again. The high cost of gas, insurance, parking and other expenses related to cars have persuaded some urbanites, at least, to give them up. And in the Portland area, Proehl said, residents are encouraged to use -- and have options for -- alternatives such as bus, train and bike.

Proehl said Oregon's growth rate appears to have stopped its decline, meaning a cycle of faster growth may be at hand.

Another expert, University of Utah professor Arthur C. Nelson, said the national economy may be "much improved" by 2013. That may lead to a population growth rebound in Oregon as people regain mobility.

"Because they cannot unload their homes in other slow-growing and declining states, many people who would move to Oregon are not able to," Nelson said by email. "It is really not entirely because of the state's economy; prospective residents who may wish to move to Oregon are motivated because their economies are worse."

Unemployment rates may not improve markedly until at least 2020, and Americans may never again have the per capita income we enjoyed in 2000, Nelson said. Those factors will slow population movement between states, but it will increase after 2012, he said.

Nelson's most recent book, "Megapolitan America," written with University of Nevada-Las Vegas professor Robert E. Lang, describes a "Cascadia" metropolitan complex stretching from Puget Sound, through Portland, to Eugene. The region, now home to 8 million people, will grow to 11 million by 2040 and continue to dominate the Pacific Northwest economy, Nelson and Lang predict.

Meanwhile, the PSU population report shows a big and small Oregon that reflects the urban-rural divide. Portland now has 583,835 people; while the metro area -- Clackamas, Multnomah and Washington counties -- has more than 1.6 million. The city of Greenhorn, in eastern Oregon's Baker County, has two people. Wheeler County, in north central Oregon, remains the least populated county at 1,435 -- fewer than one person per square mile.